From Equation REF , we can see that in order to obtain the sky intensity distribution, we need to understand and model the primary beam of the instrument (i.e. \(A(\hat{\mathbf {s}},\nu ))\) . This term determines the sensitivity and frequency dependence of the antenna and is dependent on frequency. The exact spatial and frequency structure, as well as polarization response, is complicated [1]}, [2]}, [3]}, [4]}. The situation is more complicated for instruments like MWA and SKA with an array of dipoles, whose combined beam will produce the station primary beam. The complexities of some of the beam effects can be minimized through design specifications. However, they cannot be removed completely. The beam may also show variations amongst different feeds (or dipoles for tiled arrays) due to inherent structural/positional errors or malfunctioning electronics, which adversely affect EoR observations [5]}, [6]}.
